This application claims the priority benefit of Taiwan application serial no. 89116428, filed Aug. 15, 2000.
1. Field of the Invention
The present invention relates to an apparatus for measuring valve dispensing time and the method of using the same. More specifically, the present invention relates to an apparatus for measuring the time for photoresist dispensing from the suckback valve, especially in a photoresist coating apparatus, and a method of using the same.
2. Description of the Related Art
Photoresist plays an important role in semiconductor fabrication. For example, in the etching process, the photoresist is used as mask for etching films to keep the desired patterns from being removed by etching. In the ion implantation, the photoresist serves as a mask, allow dopants to be implanted only in the predetermined regions. The photoresist used in the lithography process is liquid. The suckback valve is controlled by the electromagnetic valve on the photoresist coating apparatus to dispense the photoresist on the surfaces of the wafers from a nozzle. The wafers are arranged on a spin coater to rotate the wafers. The photoresist can be coated uniformly on the surfaces of the wafers by centrifugal force. The photoresist is made of a mixture consisting of resins, sensitization agents and solvents with various ratios. The viscosity coefficient of the photoresist varies with the ratio of the mixture set forth above.
In photoresist coating process, poor coating and planarity sometimes occurs as shown in FIGS. 1A-1E. FIG. 1A is a schematic diagram of photoresist coverage on a wafer where the photoresist in the vicinity of the center is thicker than in other regions. FIG. 1B is a schematic diagram of photoresist coverage on a wafer where the photoresist in the lower right region is thicker than in other regions. FIG. 1C is a schematic diagram of discontinuous photoresist coverage on a wafer caused by bubbles generated in the photoresist. FIG. 1D is a schematic diagram of photoresist coverage on a wafer where the photoresist in the lower right peripheral region is thicker than in other regions. FIG. 1E is a schematic diagram of photoresist coverage on a wafer where peripheral areas of the wafer lack photoresist coating. When the photoresist coating has the above defects, the yield or the reliability of the wafers are reduced, and the wafers may even fail.
The above poor coating and planarity are caused by not only the changed viscosity of the photoresist, but also abnormal condition of the photoresist coating apparatus, resulting in non-uniform thickness of the photoresist coating on the surfaces of the wafers. Due to the delay time between the suckback valve and the electromagnetic valve, the suckback vale is unable to rapidly respond to the controlling signal of the electromagnetic valve, resulting in the above abnormal condition of the photoresist coating apparatus.
Usually, if the value obtained by subtracting the maximum thickness from the thickness of the photoresist (called planarity) exceeds 100 angstroms, or in wafer fabrication, the above defects in the photoresist coating are found, the operation must stop to test and adjust the suckback valve. The conventional test and adjustment with regard to the function of the suckback valve are carried out visually and manually. When the electromagnetic valve outputs an ON signal to the suckback valve to open the lines so as to dispense the photoresist, the timer is started immediately. Then, the outlet of the nozzle is observed visually. When the photoresist begins to be dispensed, the timer is stopped immediately. The suckback valve can be determined as normal or abnormal by the time displayed on the timer. Alternatively, the displayed time can be adjusted to obtain the optimum photoresist coating. Visual and manual operation often results in human errors, and the demand for high operation accuracy cannot be satisfied.
To solve the above prior problems, an apparatus for measuring valve dispensing time which can control the delay time between the suckback valve and the electromagnetic valve to enhance the planarity of the photoresist coating and prevent the photoresist coating from generating defects, and the method of using the same.
According to one aspect of the present invention, an apparatus for measuring valve dispensing time is provided, comprising an optical fiber sensor arranged in the vicinity of the outlet of a nozzle; a first relay in which a magnetic field is generated in coils of the first relay by an ON signal from the electromagnetic valve, such that contacts thereof are connected to each other; a second relay in which a magnetic field is generated in coils of the second relay by an OFF signal from the electromagnetic valve, such that contacts thereof are connected to each other; and a stop watch including a start terminal connected to the first relay and a stop terminal connected to the second relay.
According to another aspect of the present invention, a method of measuring valve dispensing time is provided, comprising providing an optical fiber sensor in the vicinity of the outlet of a nozzle; providing a first relay; providing a second relay; and providing a stop watch. When the electromagnetic valve transmits a signal to the suckback valve to dispense the photoresist from the nozzle, an ON signal is transmitted to generate a magnetic field in coils of the first relay; at the same time contacts of the first relay are connected to start the stop watch. When the optical fiber sensor detects the photoresist dispensed from the outlet of the nozzle, an OFF signal is transmitted to the second relay to generate a magnetic field. At the same time, contacts of the second relay are connected to stop the stopwatch, with the value read from the stopwatch being the delay time between the suckback valve and the electromagnetic valve.